1. Technical Field
The present disclosure relates to a display. More particularly, the present disclosure relates to a blue phase liquid crystal display.
2. Description of Related Art
In recent years, for improving the display quality of a liquid crystal display, blue phase liquid crystals with rapid response are gradually valued, in which the blue phase represents a liquid crystal phase between the isotropic phase and the cholesteric phase and only exists in a narrow temperature range of about 1° C.
Blue phase has three different types, which are the first blue phase (BP), the second blue phase (BP) and the third blue phase (BP), in which liquid crystals of the first blue phase and the second blue phase are in a cubic form, and liquid crystals of the third blue phase are in an amorphous form and exist with a highest temperature of blue phases of the three types.
FIG. 1a and FIG. 1b are diagrams of lattice structure and disclination line, respectively, of the first blue phase liquid crystals. FIG. 1c and FIG. 1d are diagrams of lattice structure and disclination line, respectively, of the second blue phase liquid crystals. As shown in FIG. 1a and FIG. 1c, basic units of the lattice structures of the first and second blue phase liquid crystals are double twist cylinders (DTC) 100; that is, the double twist cylinders therein are arranged perpendicular with each other. Moreover, the first blue phase liquid crystals have body-centered cubic (BCC) structures, and the second blue phase liquid crystals have simple cubic (SC) structures. The disclination lines 102 of the first blue phase liquid crystals and the second blue phase liquid crystals are shown in FIG. 1b and FIG. 1d. Other than nematic liquid crystals, smectic liquid crystals and isotropic liquid crystals, the first blue phase liquid crystals and the second blue phase liquid crystals are shown as platelet texture patterns when they are viewed under a polarizing microscope.
On the other hand, the horizontal electric field produced by electrodes is conventionally used to change the refractive index of the positive blue phase liquid crystals, such that the bright/dark state of the liquid crystals changes after the light passes through the liquid crystals. FIG. 2 is a schematic diagram of the positive blue phase liquid crystals when being driven by electrodes. As shown in FIG. 2, without a horizontal electric field, the positive blue phase liquid crystals are isotropic in ideal and the refractive index change (i.e. Δn) thereof is 0 (zero). In addition, the positive blue phase liquid crystals in ideal are normally black, which herein means that the blue phase liquid crystals cannot be passed by light when the voltage is not applied thereto. Conversely, when the horizontal electric field is applied to the positive blue phase liquid crystals, the positive blue phase liquid crystals are anisotropic and the refractive index thereof changes (i.e. Δn>0), such that the light can pass through the blue phase liquid crystals and the bright state can be performed.
However, for the liquid crystal displays using the positive blue phase liquid crystals, the double twist cylinder structures of the blue phase liquid crystals are not perfect in practice, so a bit of light still can pass through the blue phase liquid crystals when the blue phase liquid crystals are in the dark state. In other words, the blue phase liquid crystals, as shown in FIG. 2, thus have light leakage in the dark state.
Moreover, since the problem of light leakage in the dark state cannot be solved by the applied horizontal electric field, the contrast ratio for the positive blue phase liquid crystal display also decreases accordingly.